Ship for transporting liquefied gases and other liquids



Oct. 26, 1965 A. s. vALK ETAL SHIP FOR TRANSPORTING LIQUEFIED GASES ANDOTHER LIQUIDS Original Filed March '7, 1960 1G Sheets-Sheet l Oct. 26,1965 A. s. vALK ETAL 35.213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7, 1960 16 Sheets-Sheet 2 IN VENTORS BY QW Mdm/M ATTORNEYS Oct.26, 1965 A. s. vALK ETAL 3,213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7. 1960 16 Sheets-Sheet 5 INV ENTORS ATTORNEYS Oct. 26, i965 A. s.vALK ETAL 3,213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch '7, 1960 16 Sheets-Sheet 4 Alm m QW. NQ@ TN.. E In E S S W u. QQ\lm wl@ .PA Wmv, K7?? Q A. F f hvvuvv s .a ik I@ rnunun BY M /Z/fjwyATTORNEYS Oct. 26, 1965 A. s. vALK ETAL 3,213,632 SHIP FOR TRANSPORTINGLIQUEFIED GASES AND OTHER LIQUIDS Original Filed March 7, 1960 16Sheets-Sheet 5 QI Q f IN V ENTORS A .5. z/Azk,

BY a@ 4M/w ATTORNEYJ Oct. 26, 1965 A. s. vALK ETAL 3,213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7, 1960 16 Sheets-Sheet 6 BY i3 Mdm ATTORNEYJ Oct. 26, 1965 A, s,VALK ETAL 3,213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIns Original FiledMarch 7. 1960 16 ShetS-Sheet 7 TNVENTOR A. 5, .AdM/r,

BY gm @Mw ATTORNEYS Oct. 26, 1965 A. s. vALK ETAL SHIP FOR TRANSPORTINGLIQUEFIED GASES AND OTHER LIQUIDS Original Filed March 7. 1960 16Sheets-Sheet 8 ATTORNEY5 Oct. 26, 1965 A. s. vALK ETAL SHIP FORTRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original Filed March 7,1960 16 Sheets-Sheet 9 ATTORNEYS Oct. 26, 1965 A. S. VALK ETAL 3,213,632SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7. 1960 16 Sheets-Sheet 10 ATTORNEYS` 0d 26, 1965 A. s. VALK ETALSHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7, 1960 16 Sheets-Sheet 11 YNVFNTO R5 ATTORNEY;

Oct. 26, 1965 A. s. vALK ETAL 3,213,632

SHIP FOR TRANsPoRTING LIQUEFIED GASES AND OTHER LIQUIDs Original FiledMarch 7, 1960 16 Sheets-Sheet 12 ATTORNEYS Oct. 26, 1965 A. S. VALK ETALSHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch '7, 1960 16 Sheets-Sheet 15 ATTORNEYS Oct. 26, 1965 A. S. VALKETAL SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS OriginalFiled March 7. 1960 16 Sheets-Sheet 14 mi; www im@ ATTORNEY Oct. 26,1965 A. s. vALK ETAL 3,213,632

'SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7. 1960 16 Sheets-Sheet 15 BYM/ Oct. 26, 1965 A. s. vALK E 'rAL3,213,632

SHIP FOR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Original FiledMarch 7. 1960 16 Sheets-Sheet 16 INVENTOKS A5. ya

BY /M MMM ATTORNEY transported over water.

United States Patent `Ofi ice 3,213,632 Patented Oct. 26, 1965 3,213,632SHP FR TRANSPORTING LIQUEFIED GASES AND OTHER LIQUIDS Allen SchulerValk, Chatham, NJ., Harry Alfred Hofmann and William FerrierKirkpatrick, Babylon, N Y., and Robert Davidson Keller, Jr., Oak Ridge,Tenn., assignors to California Texas Oil Corporation, New York, N.Y., acorporation of Delaware Continuation of application Ser. No. 13,101,Mar. 7, 1960. This application Mar. 23, 1964, Ser. No. 355,145 8 Claims.(Cl. 62-54) This case is a continuation of abandoned application, SerialNo. 13,101, filed Mar. 7, 1960.

This invention relates to the storage and transportation of liquids andliquefied gases. More particularly, it concerns the storage fortransportation of liquefied gases having low temperature boiling pointsat about atmospheric pressures simultaneously with other liquid productsof such characteristics that the vaporization thereof is not critical atnormal pressures and temperatures.

Field of invention In the transportation of liquefied gases whichrequire either high pressures for normal ambient temperatures or lowtemperatures to maintain their liquid state at about atmosphericpressure, many severe problems arise especially when it is contemplatedthat these products be Perhaps the most critical of these problems isthe difficulty encountered in making most eflicient use of the spaceavailable in the vessel or Ship carrying these products because of theextreme temperatures and pressures involved. In order to overcome theweight, size and cumbersome configurations of containers necessary tohold the liquefied gases under pressure to prevent vaporization, it hasbeen found desirable to store it on the ship at atmospheric pressure intanks properly insulated and associated with a refrigeration plant forcondensing any vapors which may evolve from the liquid. However, due tothe low density of the liquefied gas cargo it is desirable to carryother, more dense liquid cargos such as crude oil, fuel oil, gasolineand the like to utilize the full dead weight capacity of the vessel andreduce thereby this cost of liquefied gas transportation. Moreover,since liquefied gas cargo tanks will in most instances be empty onreturn trips it is necessary to provide additional tank space forballast purposes to make the vessel seaworthy. Yet, in shipconstructions known prior to this invention, no completely satisfactoryarrangements have been proposed by which these characteristics have beenfully appreciated.

Another acute problem which must be faced in the transportation ofliquefied gas on seagoing vessels is the design of an independentcontainer structure which is large enough to contain a satisfactoryquantity of liquefied gas; which is of a desirable shape orconfiguration from the standpoint of efiicient space utilization; whichis strong enough to resist `both positive and negative pressures whichmay develop due to the extremely sensitive vapor characteristics of thecargo contained therein; which may withstand the unusually largestresses imposed on the walls thereof by the temperature extremesencountered and uneven expansion and contraction as a result thereof;and further, which may withstand the stresses developed by the dynamicmovement of a ship at sea. Prior to this invention, no completelysatisfactory tank structure by which all of the requirementsaforementioned have `been fully met has been available. Also, it hasbeen found extremely difficult to satisfactorily insulate the tankswhich contain the low temperature liquefied gas so that the abnormallylow temperature will not have a deleterious effect on the surroundingship structure. In one known constructiony thermal insulation is placedcompletely over the interior of the vessel in which the containers aremounted to protect the vessel structure from the transfer of heat whichmay pass to the sub zero temperatures in the tanks. While this techniqueis satisfactory from the standpoint of providing an adequate thermal'barrier between the tanks and the ship construction, it poses an acuteproblem of repairing the interior ship hull in the event such repairbecomes necessary.

The problem of thermally insulating the tanks from the hull of the shi-por vessel is also critical to the satisfactory design of mountingdevices for retain-ing the independent tanks in place within the holdsof the vessel in which they are carried. Although this problem has beenrecognized in constructions available prior to this invention, there hasbeen no completely satisfactory solution by which both the structuralrequirements or strength necessary to hold the weight of the tanks andthe liquid therein against movement with respect to the vessel under allof the conditions which might be expected to occur, and at the same timeeffectively insulate the tank thermally from the vessel structure sothat substantially no heat leak occurs therebetween. Also, it isparticularly desirable in many instances to space the tank from thesurrounding ship structure, thereby increasing the difficulty ofproviding a suitably strong mounting which is also thermally insulative.

In addition to the foregoing, it is necessary to provide a vessel inwhich the liquefied gases are carried together with more normal liquidproducts such as gasoline or oil with a satisfactory system for handlingthe cargo during the loading, hauling and unloading operations. Exceptfor the difiiculties which might be encountered in satisfactorilyfitting a ship with the necessary pumps and piping for handling theordinary liquid cargo, this system in and of itself is of no greatconcern. In order to satisfactorily pump and handle the liquetiied gascargo on the other hand, a number of requirements must be met. First ofall, the pumping means by which the liquefied gas cargo is pumped fromthe tanks to on-shore installations, must be positioned relatively lowwith respect to the level of the independent tanks so that a suliicienthead of liquid always exists against the intake of the pumps. If thiswere not the case, low pressures would develop tending to flash theliquified gas into vapors. Another problem inicidental to the handlingof the liquefied cargo, particularly during the transportation thereof,is that of thermal stratification Within each of the tanks. This is theresult of greater pressures existing at the lower portion of the tanksunder the head of liquid therein, which higher pressures permit greaterheat absorption, thus establishing a warmer stratum of less dense liquidin the lower portion of the tanks. When this occurs, should the vesselcarrying the tanks be subjected to heavy seas, or for some other reasonshould the tanks become agitated such that the lighter liquefied gas issuddenly caused to rise in the tanks, the warmer temperatures thereofwould cause it to flash into vapors creating abnormal pressures Withineach of the tanks. A still further problem which is presented in thestorage of liquefied gases at low temperatures on transporting vesselsis the possibility of vacuums being created in the tanks due tocondensation of the vapors which might occur during conditions of lowambient temperatures present during Winter seasons for example, or dueto rapid fluctuations in barometric pressure. This problem also occurswhen unloading liquid from tanks and should such a vacuum of any greatmagnitude develop, not only would severe stresses be imposed on thewalls of the independent tanks but also, the possible admission of airthrough venting devices could produce such detrimental efiects asintroduction of moisture and mechanical malfunctioning due to freezingthereof, the formation of combustible mixtures and the like. Prior tothis invention, the lack of means for overcoming these problems ofpressure excesses has resulted in reliance on safety relief valves bywhich abnormal pressures beyond a very slight variation from atmosphericpressure are vented into the air. While such devices effectively controlthe pressures existing within the tank, they result in substantiallosses of cargo, not to mention the fire hazards created by theextremely combustible mixture of the gas vapors and air in and about theship.

Objects A principal object of this invention is to provide a new andimproved vessel for simultaneously transporting liquefied gases havinglow temperature boiling points along with other relatively non-volatileliquid products at normal temperatures at normal pressures, by which theproblems previously encountered are effectively and substantiallyovercome.

Another object of this invention is the provision of a vessel in whichliquefied gases may be transported at or about atmospheric pressures attemperatures corresponding to their boiling points, the vessel hullbeing effectively insulated therefrom and as well as capable ofcontaining other liquid cargo or, if desired, sea water for ballastpurposes.

A fur-ther object of this invention is that of providing a vessel inwhich liquefied gases may be transported at or about atmosphericpressures at temperatures corresponding to their boiling points in amanner such that tanks containing the liquefied gas are within fiuidimpervious holds to effect emergency containmen-t of the liquefied gasand such that cargo and ballast tanks in the hull of the vessel protectthe liquefied gas tanks from collisions.

An additional object of this invention is the provision of a new andimproved tank for containing liquefied gases and receivable within thehull of a sea going vessel in a manner such that maximum use of thespace therein is obtained.

A further object of this invention is the provision of a tank of thetype referred to which is resistant to stresses imposed by both negativeand positive internal pressures and which is also resistant to stressesimposed by differential amounts of thermal expansion and contraction andwhich will withstand the dynamic loads imposed by the movement of avessel at sea.

A further object of this invention is that of providing a vessel of thetype referred to with means for effectively mounting independentliquefied gas containing tanks therein in a manner such that no metal tometal contact exists between the vessel and the independent tanks andyet in a manner such that the independent tanks are immovable withrespect to the vessel under the most extreme conditions.

Another object of this invention is the provision of means 'for mountingindependent liquefied gas containers within a sea going vessel in amanner such that thermal expansion and contraction of the tanks in noway affects securement of the containers within the vessel.

A further object of this invention is the provision of extremelyeffective thermal insulation for insulating the cold liquefied gascontainers from the vessel structure in a manner such that the usualmaintenance requirements of the vessel are not impaired in any Way.

Another object of this invention is the provision of a vessel of thetype referred to equipped with means for effectively handling both theliquefied gas cargo and the other liquid cargo during loading, unloadingand transporting operations.

A further object of this invention is that of providing a vessel of thetype aforementioned with a refrigeration system operative in accordancewith pressures existing within the liquefied gas containers to condensevapors that may be evolved therein and thus maintain the pressuresexisting within the containers at or about atmospheric pressure withoutloss of cargo.

Another object of this invention is the provision of a vessel of thetype referred to in which liquefied gas may be transported withoutdanger of thermal stratification and the resulting pressures incidentalthereto.

A further object of this invention is the provision of a vessel fortransporting liquefied gases at atmospheric pressure, which vessel isequipped with means for preventing the occurrence of abnormal vacuum ornegative pressures within the liquefied gas containers.

A still further object of this invention is the provision of a vessel ofthe type referred to equipped with refrigeration means to facilitate thetransportation of liquefied gases thereon as well as with means forgenerating vapors from the liquefied gas under conditions of extremelylow ambient temperatures, thereby preventing damage to the refrigerationequipment land possible negative pressure in the cargo tanks.

Other objects and further scope of applicability of the presentinvention will be apparent from the detailed description givenhereinafter. It should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, isgiven by way of illustration only since it will be made apparent tothose skilled in the art that various changes and modifications can bemade without departing .in any way from the true spirit and scope ofthis invention.

General description In general, the aforementioned objects areaccomplished by a ship or vessel construction in which the hull isformed having an exterior shell and a fluid impervious wall spacedinwardly therefrom on each side as well as an upwardly spaced, fluidimpervious fioor thereby establishing wing and fioor tanks adaptable forthe storage of ordinary liquid cargo such as oil, gasoline or the like.The hull is yalso divided longitudinally by a plurality of transversebulkheads which define with the wing tanks, fluid impervious holds inwhich independent tanks for containing liquefied gases at atmosphericpressure and at sub zero temperatures may be mounted and which holds arecapable of containing the liquefied gas in the event the independenttanks develop a leak or otherwise become defective. The tanks areinternally reinforced in a manner -so as to resist negative and positivepressures which develop incidentally to the handling of liquefied gasesas well `as to accommodate the variation in thermal expansion andcontraction resulting from the temperature extremes involved. The tanksreceive on their exterior surfaces, suitable thickneses of thermalinsulation so that the ship hull is not exposed to the extremely lowtemperature of the liquefied gases and the danger of weakening as aresult thereof. The tanks are mounted in the hold of the ship hull insuch a manner that all forces are resolved into compressional or shearstresses in blocks of thermally insulating material, therebyeli-minating all metal to metal contact between the ship hull and theindividual containers.

The vessel is provided with a pump room in which cargo pumps areprovided for independently unloading the wing and floor tank cargos andthe liquefied gas containers. In addition, the presure within theliquefied gas containers is maintained by either a vaporizer or arefrigeration system depending on the nature of pressures existingwi-thin the tanks.

The refrigeration equipment is used to condense vapors evolved .in thetanks and thereby lowering the pressures existing therein while undersome conditions, such as during the unloading operation and duringconditions in which low ambient temperatures exist, the vaporizer iscapable of vaporizing the liquefied gases to raise the pressure in thesetanks and thereby alleviate the possibility of damaging negativepressures of vacuums. Also,

the vaporizer -may be used in conjunction with the refrigeration systemto impose an artificial load on the refrigeration units to preven-t thenecessity for shutting off the refrigeration equipment as well as toprevent the damage which might result thereto upon continued runningwith no refrigeration load. In addition to the vaporizer andrefrigeration unit, the vessel-is equipped with suitable pumping andconduit means by which the liquefied gases are recirculated and therebycontinuously stirred to prevent thermal stratification.

A more complete understanding of the new and improved vessel of thisinvention and its operation may be had by reference to the accompanyingdrawings, in which:

FIG. 1 is a side elevation of the vessel illustrating the generalarrangement of various units therein;

FIG. 2 is a diagrammatic plan view of the vessel shown in FIG. 1;

FIG. 3 is an enlarged cross-section View taken along lines 3-3 of FIG.2;

FIG. 4 is an enlarged fragmentary cross-sectional view of the vesselhull;

FIG. 5 is a plan View of the independent liquefied gas tanks of thisinvention with a portion of the top cut away to illustrate the interiorthereof;

FIG. 6 is an enlarged fragmentary horizontal crosssection of the tankillustrated in FIG. 5;

FIG. 7 is a fragmentary cross-section taken along lines 7 7 of FIG. 6;

FIG. 8 is a fragmentary cross-section taken along line 8 8 of FIG. 6;

FIG. 9 is a fragmentary plan view of the floor of the tank shown in FIG.5;

FIG. l0 is a fragmentary cross-section taken along line III-10 of FIG.9;

FIG. 11 is an enlarged fragmentary view looking up at the top of thetank shown in FIG. 5;

FIG. 12 is an enlarged fragmentary cross-section taken along line 12-12of FIG. 11;

FIG. 13 is a fragmentary transverse cross-section of the tank top takenalong line 13-13 of FIG. ll;

FIG. 14 is a fragmentary elevation of the transverse swash bulkhead ofthe tank shown in FIG. 5;

FIG. l5 is a side elevation in partial cross-section showing the new andimproved tank mounting devices of this invention;

FIG. 16 is an enlarged fragmentary cross-section taken along line 16--16of FIG. 15;

FIG. 17 is an exploded perspective View illustrating the mounting deviceadaptedto support the center of the tank shown in FIG. 5;

FIG. 18 is an enlarged cross-sectional elevation of the mounting deviceshown in FIG. 17 and taken along line 18-18 of FIG. 19;

FIG. 19 is a cross-section taken along line 19--19 of FIG. 18;

FIG. 20 is a fragmentary plan View showing an auxiliary mounting devicefor the tank within the hold of the vessel;

FIG. 21 is a cross-sectional view taken along line 21-21 of FIG. 20;

FIG. 22 is a fragmentary cross-section view of the auxiliary mountingdevices taken along line 22-22 of FIG. 21,'

FIG. 23 is an enlarged fragmentary plan view illustrating the liquefiedgas handling deck piping on the vessel of this invention;

FIG. 24 is a fragmentary elevation showing the liquefied gas handlingpumps, piping and refrigeration equipment in the vessel of thisinvention;

FIG. 25 is a partial plan view taken along line 25-25 of FIG. 24 andillustrating the liquefied gas condensate return and recirculating pumpsas well as the piping therefor;

FIG. 26 is a plan View taken along line 26-26 of FIG. 24 illustratingthe liqueed gas cargo pumps of this invention;

FIG. 27 is a fragmentary plan view showing schematically the piping forthe liquefied gas containing tanks of this invention;

FIG. 28 is a fragmentary plan view showing the deck piping for handlingregular liquid cargo in the bottom and wing tanks of the vessel of thisinvention;

FIG. 29 is a plan view showing the car-go pumps and piping for loadingand unloading the regular liquid cargo to and from the vessel of thisinvention;

FIG. 30 is a flow chart showing dramatically the refrigertion system ofthis invention during the loading operation;

FIG. 31 i-s a similar View showing the operation of the refrigerationsystem at sea;

FIG. 32 is a flow chart illustrating diagrammatically the refrigerationsystem for the vessel of this invention during unloading operations.

DETAILED DESCRIPTION The general arrangement and hull structure Thegeneral arrangement of the vessel to which this invention relates asshown in FIGS. l, 2 and 3 of the drawings includes a bow section 10, amidship section 12 Iand a stern section 14. The deck is of aconventional design having a midship-house 16 and a deck-house 1S aft onthe stern section 14. In a generally central position on the deck ismounted a vent mast 20 which is connected with the liquefied gas systemthrough relief valve devices in a manner which will be more fullydescribed hereinafter. Likewise, the bow and stern sections aregenerally of conventional construction except that in the fore portionof the stern section a pump room 22 is provided Which communicates witha refrigeration machine room 24 by way of a vertical passage 26.

The midship section of the vessel is separated into a plurality of holds28 by transverse bulkheads 30 to enable a .plurality of independentliquefied gas holding tanks 32 to be received herein. The hull structureof the vessel in which the holds 2S are positioned is formed having anouter shell 34 and inner vertical Walls 36 which not only establish thetransverse dimensions of the holds 28 but also serve with the shell assidewalls of Wing tanks 28 adapted to receive relatively non-volatileliquid cargo such as oil, gasoline or the like, of these tanks may beused to hold sea water ballast. It will be noted that the holds 28 inwhich the independent tanks 32 are received are,'in effect, secondarytanks capable of containing the liquefied gas in thel event the tanks 32develop a leak or are otherwise damaged. This is essential in ships usedto transport liquefied gas both from standpoint of safety and because itis required by governmental regulations. In a similar manner, a bottomfioor 40 is spaced upwardly of the bottom shell to establish bottomcargo tanks 42. The wing tanks 38 as well as the bottom cargo tanks 42are seprarated longitudinally by extensions of the transverse bulkheads3G. Thus, it will be seen that the midship section of the hull is madeup of a series of wing tanks 38 aligned longitudinally of the vessel asWell as the bottom cargo tanks 42 situated between the bottom shell andflooring of the vessel. Not only does this construction permit theeconomic advantages of a double pay load to be realized as well asenhancing the seaworthiness of a lightly laden ship, but also these wingand iioor tanks, when filled, constitute a protective barrier for theliquefied gas tanks in case of a collision.

A better understanding of the hul-l structure aforementioned may be hadby reference to FIG. 4 of t-he draw-ings which illustrates thestructural details thereof. In accordance with convention-al practice,the shell is formed having a bottom plate 43 connected to side plating44 by the usual bilge strake 46. Likewise the upper portion of the sideplate 44 terminates in a sheer strake 48. The shell yis su-it- '7 ablyreinforced by longitudinally extending stiieners 50 which preferablytake `the form of inverted L-shaped members. The vertical wal-l 36 isconstructed in a manner similar to the shell 34 in that it takes theform of a plate reinforced by longitudinal stilfening also comprisinginverted L-shaped members 52. This same construction is carried onthroughout the flooring 40. In order to provide additional strength `andreinforcing as well as to suitably baffle the liquid retained in thewing tanks 3S, transverse web plates 54 are atiixed at their edges t-othe inner wiall 36 and t-he shell 34. The transverse web, as can be seenin FIG. 4 is provided with rectangular cutout-s S6 t-o receive theinver-ted L-shaped stiteners 50 and 52 in the `outer shell and wallrespectively. Further, the web 54 is for-med having apertures 58 toprovide `communication within the wing tanks for filling and emptyingoperations.

In like fashion, the bott-om portion `of the hull is reinforced Withvertical ywebs 60 Ahaving apertures 62 cut therein. Also, it will benoted that both the transverse web plates 54 and 60 are provided withtransverse stitening members 64.

The deck is formed having a deck plate 66 suitably reinforced bylongitudinally extending inverted L-shaped members 68, Iall of which issupported by a fabricated transverse girder 70. The girder 70 is of aconventional design and comprises -a web 72, flange 74 and verticalstitening vbrackets 76. Also, it will be noted that the deck plate isprovided with a hatch opening or aperture 78 through which -acce-ss maybe lhad to the liqueed gas tanks positioned thereunder as will be morefully understood from the description which follows below.

The liquefied gas holding tanks The individual -liquetied gas holdingtank structure will be most clearly understood by referring to FIGS.through 13 in the drawings. As shown in FIG. 5, each tank is constructedhaving a pair of sidewalls 80, a pair of end walls 82, la .bottom `84and -a top y86. Also, the tanks are divided longitudinally by atransversely extending swash bulkhead 88.

As shown in FIGS. 6, 7 and 8, the side and the end walls 80 and 82respectively are formed having respective exterior shells or plates 90and 92. In both instances, the plates 90 and 92 are directly attached toand supported by a plurality of vertically extending stiffeners 94 whichare in the form of inverted L-shaped members. The shells 90 and 92 arefurther supported by horizontal webs 96 and 98 suitably stiffened byangle members 100 and having at their free edge a continuous flange 102,thus effecting a continuous girder structure. As shown most clearly inFIGS. 7 and 8, a plurality of horizontal webs or girders 96a, 98h, 98C,98d are positioned in vertically spaced relationship along the interiorof the side wall 80 and likewise a plurality of webs 98a, 9817, 98C, 98dare provided on the interior of the end Wall 82. To support the interiorends of the transverse webs 96 and 98 and thereby retain themperpendicularly to the walls for maximum strength, angular bracketmembers 104 are provided substantially as shown.

It will be noted that the lower web members 96C, 96a', 98e and 98d arespaced to be closer together than the upper members 96a, 96b, 98a and9817. The reason for this is that due to the head of liquid in the tankunder normal, loaded conditions the forces acting yon the lower portionof the vertical walls will be greater. Thus, the increased strengthafforded by the more closely positioned reinforcing Webs 96C, 96d, 98oand 98d will be appreciated. Also, since the webs 96 and 93 arecompletely independent `of one another, there is no tendency forabnormal stresses to develop in the wall structure due to uneventemperatures existing vertically along the walls and the resultingexpansion or contraction therein. In other words, the entire wallreinforcing structure is free to move with any change in dimensionswhich might occur in the walls and yet, under all conditions, the tankwall structure will resist equally well, internally and externalpressures.

The tank bottom as shown in FIGS. 9 and 10, is formed having a bottomshell 106 directly backed up by a plurality of evenly spacedtransversely extending inverted L-shaped members or stiffeners 108.Extending longitudinally of the tank are several girders 110 fabricatedfrom a web 112 having cutout portions 114 to receive the transversemembers 16S and terminating at its upper end in a iiange 116. The web112 may be further stiiened by brackets 118.

The tank top is constructed in a manner similar to the tank bottom inthat it is provided with a shell directly supported on L-shaped membersor stiffeners 122 extending transversely thereof and provided withhatches or openings 121, on diagonally opposite corners. Longitudinalgirders 124, having a web 126 out out at 128 to receive the L-shapedmembers 122 are provided along lines coinciding with the linesestablished by the bottom girders 110. Also, each of the girders 124 isprovided with a ange 130 at its lower edge and is suitably stifiened byvertically extending angle members 132. As shown in FIG. 13, the beams124 may be supported against lateral displacement by brackets 134extending between the lower edge of the girders 124 and terminating at apoint adjacent the top plate 120.

The details of the transverse swash bulkhead 88 may be best understoodby referring to FIGS. 6 and 14 of the drawings. As shown, the bulkheadpreferably consists of a vertically extending plate 136, having aplurality of apertures 138 to permit only a restricted movement ofliquid therepast. The plate 136 is reinforced by alternate angle members140 and H-shaped members 142. The H-shaped members 142 are centered inthe plane of the plate 136 and are anchored at their lower end `on thelongitudinally extending floor girders 112. Since the longitudinallyextending top girders 124 are located in substantially the same plane asthe bottom girders 112, these girders are supported at their mid pointson the H-shaped members 142. To provide adequate transversereinforcement, the plate 136 supports a plurality lof horizontallydisposed webs 144 which, as may be seen in FIG. 6, are continuations ofthe webs 96 and 98 on the side and end walls 80 and 82 respectively.

It is to be understood that the material from which all structuralcomponents of the tanks 32 are fabricated retains its strength at thelow temperatures at which the liquefied gas is stored. For example, forrelatively mild temperatures, low alloy nickel steel maybe used whereasstainless steel or aluminum may be required if extremely lowtemperatures are contemplated.

As shown in FIG. 5 the tanks 32 are covered with a suitable thickness ofthermal insulation 146 to isolate the cold temperatures within the tanksfrom the ship hull and as well, to prevent the leakage of heat into thetanks in amounts such that abnormal refrigeration loads are avoided. Itis preferred that the insulation consist essentially of a plastic foamsuch as urethane foams or cellular glass block suitably cushioned.However, other thermally insulative materials may be used, such as forexample, iber glass, balsa wood, mineral wool, cork, glass wool and thelike.

T he tank supporting devices To support the tanks 32 properly withintheir respective holds 28, the tank mounting devices illustrated inFIGS. 15 through 22 are preferred. In the form illustrated in FIGS 15and 16 a plurality of depending brackets are Welded, riveted, bolted orotherwise affixed to the tank bottom plate 106. The depending bracketseach comprise a web portion 172 suitably stitfened by a plurality ofange-like stiteners 174, and terminate in inclined lower ends to whichan inverted channelshaped member 176 is afxed. Received within the open

2. A TANK FOR CONTAINING AT ABOUT ATMOSPHERIC PRESSURE LIQUEFIED GAS ATLOW TEMPERATURES COMPRISING BOTTOM, TOP, SIDE AND END WALLS OF GENERALLYRECTANGULAR CONFIGURATION; EACH OF SAID WALLS INCLUDING A SUBSTANTIALLYSMOOTH EXTERIOR, FLUID IMPERVIOUS PLATING; A PLURALITY OF PARALLEL,GENERALLY VERTICAL STIFFENERS ON THE INTERIOR OF SAID PLATING; AND APLURALITY OF GIRDERS EXTENDING GENERALLY PERPENDICULARLY TO SAIDSTIFFENERS, SAID GIRDERS BEING CUT OUT AT THEIR INNER EDGE TO RECEIVESAID STIFFENERS, THE SPACING OF SAID GIRDERS ON SAID SIDE AND END WALLSBEING GREATER AT THE UPPER PORTION OF SAID WALLS THAN AT THE LOWERPORTION THEREOF.